The invention concerns a stent for the treatment of pathological body vessels, which can be introduced into the body vessel in the form of at least two longitudinally extended filaments by means of an implantation device and assumes its predetermined form only at the site of implantation after the implantation has been carried out.
The introduction of spiral stents of metal or plastic into a diseased body vessel for treating pathological body and blood vessels is known. Such treatments are considered for diseased vessel occlusions or aneurysms, particularly of the aorta. The implantation of such vessel prostheses is made difficult due to the considerable diameter of these prosthesis. For the most part, only one surgical implantation of the vessel prostheses is possible in combination with an opening of the vessel and a subsequent vessel closure by means of a vessel suture. In the case of treatment of an aortic aneurysm, stents are introduced by means of the pelvic arteries. This treatment is made difficult or is completely obstructed by stenoses occurring principally in combination with aortic aneurysms and by the serpentine course of the pelvic arteries.
In the named cases, but also in the case of treatment of small vessels, such as intracranial vessels, it is advantageous to use stents, which can be widened from a small diameter present during the implantation to a larger diameter at the implantation site. It is provided accordingly to implant balloon-expandable and self-widening stents with a suitable catheter in the vessels to be treated. However, up to the present time, the named stents have still not fulfilled the technical prerequisites for a problem-free insertion.
Thus, for example, in the case of the so-called IN stent, this involves an elastic spiral, which is kept at a smaller diameter during introduction in the body vessel by the catheter, is released from the catheter at the site of implantation by means of a special mechanism, and then widens to its diameter of use.
Here, there is the disadvantage that the diameter of the spiral stent is at most double in the widened state when compared with the initial state, whereby relatively large puncture openings are necessary for introducing this type of stent. In this connection, the use of a thermo-memory wire has already been described in the paper xe2x80x9cTransluminally placed coil spring endarterial tube graftsxe2x80x9d, Invest. Radiol. (1969) No. 4, pages 329 ff. by Charles Dotter.
Thermo-memory wires are for the most part Nitinol wires, i.e., thus nickel-titanium alloys, which are brought to a predetermined form at temperatures between 400xc2x0 and 500xc2x0 Celsius, and keep this form up to a determined transformation temperature below body temperature.
The xe2x80x9cthermo-memory propertyxe2x80x9d is understood to mean that these wires lose their previous form and elasticity by an appropriate subsequent cooling, for example by means of ice water, and then are freely movable as longitudinally extended wire and are flexible. As soon as the wire has again warmed up to a temperature approximately corresponding to body temperature, such a wire springs back in a fully elastic manner into the spatial form impressed during the heat treatment.
Charles Dotter has proposed to implant a spiral stent from cooled thermo-memory wire in the form of a longitudinally extended wire, which then springs into the desired spiral and prosthetic form at the site of implantation, due to its described thermo-memory property. It has been shown that such simple coiled stents in their predetermined state have law stability and are also difficult to introduce and to place exactly.
A stent is known from WO 94/03127, in which several wire filaments that are longitudinally extended in an introductory shape assume in their predetermined state an undulating form that conforms to the vessel wall, whereby the wavy lines of two filaments are shaped each time such that a network comprised of approximately oval elements is formed. The stability of this network can be increased further in that wavy lines lying opposite one another are joined together at sites where they approach one another.
It is a disadvantage in this network-type stent that the implantation of such a complicated structure leads in particular to considerable difficulties in the case of greatly curved vessels. In addition, the construction of such a stent made of a multiple number of individual filaments requires a catheter with a relatively wide introduction diameter. Further, in this above-described stent, each time there is only one single predetermined diameter in the expanded or widened state. It is thus difficult to adapt the stent diameter to the diameter of the artery to be treated.
The object of the present invention is thus to create a stent of the above-named type and functional purpose, which is characterized by a high stability as well as a simple handling during implantation and, in addition, has a high rate of expansion, i.e., a particularly high ratio of stent diameter in the expanded state to stent diameter in the introduction state.
This object is resolved in a stent having at least two filaments in the form of opposing spirals over at least one part of the longitudinal extent of the stent. The stent according to the invention thus exists in its predetermined state of at least two spirals, which are arranged opposite one another, thus in opposite rotational direction, and has the outer form of a tube. It is this double-spiral stent with filaments in the extended state, thus with a nearly one-dimensional structure, which is introduced.
A stent formed in this way has a high stability with a simultaneous high flexibility. The pitch of the individual spiral loops can thus be greatly modified over the entire length of the stent. This makes possible, in particular, a placement of the stent in greatly curved body vessels, without having to contend with adversely affecting the stability of the stent or damaging the lumen of the body vessel, if it becomes constricted, even if only in segments. The entire length of the stent body can also be modified due to the variability of the pitches of the individual spirals. In this way, for example, an improved anchoring of the stent within the body vessel can be achieved. Further, a varying load capacity or support capacity of the stent each time adapted to the vessel can be achieved in the treatment of vessel disorders, such as, for example, aneurysms. Spiral loops with smaller pitch, thus of higher density, are required roughly at the ends of an aneurysm stent in order to anchor the stent here, while in the region of the aneurysm itself, fewer spiral loops are required.
A particularly careful and simple implantation of the stent is then possible, if the filament is produced from a thermo-memory wire. In this connection, in particular, the use of Nitinol(copyright) wires is recommended. However, plastic filaments with suitable thermo-memory properties can also be used. Instead of the filaments produced from thermo-memory wire, high-elastic to super-elastic wires may also be selected as filaments, which arrive at the site of implantation in their predetermined spiral form, due to their special elastic properties. Such a filament can also be produced from Nitinol, from special steel, or also from suitable plastics.
Appropriately, there are two filaments, each time forming a coil of a single filament wire, which has a sharp bend, an arc-shaped piece or a loop roughly at the distal end of the stent, such that the configuration of two opposed spirals is made possible. Such a design has a high stability.
Instead of producing the double-spiral structure of the stent according to the invention from one filament wire, which is bent correspondingly into the shape of opposed spirals, it is also possible to cut the double-spiral structure of the stent from a tube-shaped workpiece. The cutting out can be produced very efficiently by means of a laser. The particular advantage of this configuration lies in the fact that the opposed spirals are already joined with one another at their crossover points, whereby possible additional connection means are not necessary.
A further stabilizing action of the stent is achieved by joining together two spirals constructed of individual filaments roughly at the distal end of the stent. This joining can be produced by gluing, soldering or welding the two stent wires, or also, however, this may involve a sleeve, which engages over the two stent wires and thus produces a connection, which permits a limited axial displacement of the stent wires, but prevents a rotation of the stent wires opposite one another. The flexibility of the stent is also improved in this way. An appropriate connection may also be present at the proximal end of the stent.
Advantageously, these connection points of two spirals are found on the outer periphery, thus on the envelope of the tube-shaped stent. In this way, a disruption of the blood flow flowing through the body vessel is kept as small as possible. Advantageously, the connection sites are bent outward radially, so that in no case do they project into the lumen. In particular, in a curved course of the vessel, the ends of the stents are adapted to the curved course of the body vessel by such a design.
In order to further increase the stability of the stent, the opposed coils are combined with one another at least partially at points where the coils cross each other. A particularly advantageous connection is produced by threads of good biological compatibility, perhaps nylon threads, which are combined with one of the spirals, and which have loops at the pregiven places, through which the other loop is passed each time. Such a configuration makes possible the evolution without problem of the double spiral during the implantation. In order to avoid friction between the spirals or between the spiral and the tissue, which could lead to wear and tear of the filaments, or to tissue irritations, the spiral loops should be joined solidly with one another such that in the predetermined state, the possibility of movement of the spirals opposite one another is reduced to a minimum.
In another embodiment, the stent possesses three or more filaments. While two of the filaments are present with preferably equal pitch in the stent in the above-described way in their predetermined form, as opposed spirals, the remaining filaments that are also configured in spiral form run with a different pitch than the two opposed spirals. In this way, the third filament runs or the subsequent filaments run at least partially in the gaps opened up by the opposed double spirals. Overall, the stability of the stent is further increased and also a uniform lumen is assured for the most part over the total length of the stent.
Even if the construction of the stent from two opposed spirals is of high stability and flexibility, however, it can in some cases still be advantageous, if the stent is comprised of a double spiral which is spiraled over a part of its length in the same direction rather than in opposite directions. In this region, crossovers of the filaments with one another do not occur. Also, there is a still further increased flexibility in these segments in the stent, which, for example, is of advantage for implantation in greatly curved vessels.
In another embodiment, an improved spring effect results in the longitudinal direction of the stent. Such a stent not only has higher carrying capacity and support capacity, but it also has a higher body compatibility, particularly in the case of an implantation in a curved or flexed region of vessels.
An advantageous further development is produced, if each time, two filaments have the same type of arc-shaped segments opposed to one another at least over a part of the longitudinal extent of the stent.
Advantageously, arc-shaped segments of two filaments opposed to one another are joined together. Thus, the arc-shaped segments can be hooked with one another, or interlocked in a type of fence-like wire mesh, whereby a higher flexibility and stability of the stent is achieved. A particularly flexible, but still stable connection is produced by textile threads, which are joined rigidly with one filament, and which have loops taking up the other filament each time. Such a form of embodiment particularly facilitates manipulation when the stent is introduced in the form of longitudinally extended filaments. At the same time with such a joining, an axial mobility of the filaments opposite one another is assured, which in turn is of advantage in the region of greatly curved body vessels. Alternatively, however, for the flexible joining of the arcs under one another, a rigid connection is also possible, by means of sleeves, for example, which engage over both arcs or, by welding, soldering or gluing. Also, a combination of sleeves and other of the named fastening possibilities is conceivable. When the arcs are rigidly joined with one another, the introduction radius through the catheter can be kept particularly small.
A particularly advantageous embodiment involves, the filaments of the stent having an alternating form of arcs and spirals and are displaced relative to one another such that each time an arc crosses a spiral loop. A nearly rectangular crossover occurs thereby, whereby the stability of the stent is further improved. Preferably at the predetermined crossing point, one of the filaments has a small out-buckling, in which the corresponding filament can be taken up. The corresponding filaments engage in these places in their predetermined state, which leads to a still further increase in stability.
Appropriately, the stent is adapted in cross section in its predetermined state, to the body vessels for which it is provided. Thus it may be advantageous to provide an oval or elliptical lumen of the stent, at least in segments. Another lumen shape is necessary, for example, for the proximal part of the stent in the common carotid artery or in the bulb of the internal carotid artery, while the distal end must have a smaller diameter, since the artery cross section generally tapers here.
In another embodiment, the stent is used as a double stent. Thus only one segment of the stent has an individual tubular form of the previously described type. In a second segment, on the other hand, the stent has two lumina, which are supported each time by at least one spiral-shaped filament and which contact one another partially. Thus a double stent is constructed over at least one part of the longitudinal extent of the stent. The lumina of the two secondary stents can be constructed ovally, as described above, or, however, they may have the cross sections of two xe2x80x9cDxe2x80x9d pieces, which are a mirror image of one another. At their places of contact, the two secondary stents can be combined with one another, as previously described and depending on the type, by threads, which are attached to at least one of the filaments and have loops, in which the other filament is taken up each time. It is also possible that the two spirals of the double stent consist of filaments, which are arranged such that the loops, viewed in their cross section, have the form of a xe2x80x9cfigure eightxe2x80x9d, thus they cross over. In such an embodiment, an attachment of the two secondary stents with one another is not necessary.
The stents with the above-described features, are covered with a deformable membrane sheath on the outer or inner side of the double-spiral structure. The membrane is thus attached each time to the ends of the stent and is not present in the predetermined state, i.e., the expanded state of the stent under longitudinal tensile load. If the stent is pulled in length, the membrane is correspondingly extensible. As an advantageous material for such a membrane, for example, highly elastic plastic, silicone or latex are considered. Alternatively to elastically deformable membrane sheaths, however, a knitted fabric or a continuous knit can be utilized, whose meshes can be converted, upon implantation of the stent, from an introductory shape, in which the threads of the textile fabric run essentially parallel to the stent axis into an expanded form, in which the threads forming the meshes are essentially perpendicular to one another. Also, the threads of such a knitted fabric can be textured, i.e., have an expandable, spiral-shaped structure.
Particularly advantageous is the use of textile material, such as, for example, elastic fabric or polytetrafluoroethylene (PTFE), which also can be extended correspondingly. In this case, the open meshes of the fabric would be rapidly closed by thrombosis, so that also in this case a closed wall forms.
In order to prevent the textile fabric in the extended state of the stent from penetrating between the stent filaments into the inner region of the stent, metal threads that are preferably crossed are worked into the fabric structure of the textile membrane sheath, and these threads prevent the textile from entering into the region between the stent spirals.
Another advantageous possibility for providing a stent with a sheath in which, the stent has the form of a wire loop skeleton, whose individual double spiral loops are screened by fabric structures or fibers joined with the filaments opposite the vessel wall. The stent body is thus formed only in part by the filament and the rest of it is comprises fibers or fabric segments.
By screening the filaments relative to the vessel wall by means of the fabric structures/or fibers, the body compatibility of the stent is considerably increased. Such a stent thus corresponds to a stent graft. A decisive advantage of the further development of the invention according to claim 24, however, lies in the fact that, unlike the previously known wire stents with wire loops contacting one another in the region of the fabric and fiber segments, the walls of the stent unit have membrane properties, thus for example, a diffusion capability. The vessel walls can be thus be further accommodated in a path of diffusion. Additionally, a local administration of medication, is possible by coating the medication onto the novel stent wall. The danger of a possible intimal hyperplasia or another neoplastic proliferation of the vessel walls to be treated is reduced in this way. Another advantage can be seen in the fact that a reinforced accumulation of connective tissue cells or a reinforced thrombosis results in the region of the fabric or fiber segments of the stent wall. In distinction from known embolization spirals for sealing vessels according to Gianturco, the stent according to the invention specifically forms a tube provided with fibers, which leaves open the vessel volume. Based on the described cell accumulations, a biological wall is gradually formed as a consequence of the thrombogenicity of the fabric structure or of the fibers. Finally, it is possible to prepare the fibers in such a way that they can deliver medication, perhaps for producing thrombi, after successful implantation, in order to achieve a sealing of the walls of the stent body as rapidly as possible.
It is particularly advantageous, if the fabric structures and/or fibers proceeding from different spirals and/or arc segments come into contact at least partially with their free ends. In this way, the wire filament is surrounded by a sheath of fibers and/or fabric structures. Based on the described cell accumulation, this promotes the formation of a biological wall due to the thrombogenicity of the fabric structure or of the fibers. For example, aneurysms can be sealed off in this way from the normal blood flow, whereby the danger of a rupture of the aneurysm is effectively eliminated, or at least is considerably reduced. The treatment of aneurysms is particularly advantageous when these are present in the abdominal aorta in the infrarenal segment, but also for small intracranial aneurysms.
The stent can be produced without the use of foreign adhesives, which are of doubtful stability and body compatibility, so that at least one filament including the fabric structures or fibers is sheathed and/or enveloped. This sheathing or enveloping can be produced by means of another textile or thread. An additional fastening of the fabric structures or fibers is not necessary.
In another embodiment of the invention, the fastening of the fabric structures or splitting fibers can be produced simply by interweaving a filament from several filaments as the filament, whereby the fabric structures and fibers are maintained within the interweavings of the individual filaments. The fabric structures and/or fibers are thus passed through openings, which are present between the filament parts interwoven with one another. Instead of this, it is also possible to provide openings in a filament, through which the fabric structures and/or fibers are drawn. At least with such a form of embodiment, the filament appropriately has a rectangular cross section. Also, in the case of this embodiment, the use of additional adhesives or other fastening means for the tissue structures or fibers is not necessary.
Appropriately, fabric structures and/or fibers extending radially from one filament are of different lengths in segments and/or according to radial direction, corresponding to the requirements of the respective body vessel.
In a particularly advantageous configuration, the fabric structures and/or the fibers are attached to the filaments such that their free ends contact each other, at least approximately, with the formation of a wavy line-shaped boundary line. In the transition to the predetermined state, a particularly advantageous adaptation of the sheath of fabric structures and/or fibers to the spiral structure is thus assured.
A particularly compact and rigid stent sheath is produced by overlapping the fabric structures and/or the fibers, at least partially, between the individual adjacent spirals and/or arc segments formed by the filaments.
The fabric structure of the stent can be produced from a textile as well as a metal in order to produce membrane segments capable of diffusion. When textile fabrics are used, the membrane segments have smaller pores and when metal fabrics are used, they have larger pores. In the case of small-pore fabric segments, thrombosis is produced and the organization of the introduced structures is accelerated. Metal fabric structures, on the other hand, have a higher crosswise stability. However, a combination of metal and textile fabric structures can also be meaningful.
The crosswise stability of such a stent can also be increased by cutting the fabric structures in the form of a fringe, at least in segments. The fabric structures can be overlapped and interlocked in a reinforcing and compacting manner with an appropriate length of fringe.
The same objective may also be achieved in that the fabric structures are provided with an adhesive agent, preferably a Velcro(copyright) seal, in order to join the fabric structures overlapping with one another. The use of appropriate Velcro(copyright) strip seals also assures that the longitudinally extended filaments achieve their spiral shapes at the site of implantation. This adhesive effect can also be achieved by arranging thin fabric strips, which have alternating xe2x80x9chooks and eyesxe2x80x9d according to a type of Velcro(copyright) seal strip on the filament.
According to patent claim 35, due to the fact that the cross section of the fabric structures used decreases outwardly with increasing distance from the respective filament, it is assured that the stent also has an essentially uniform outer diameter even in the region of the overlappings. Appropriately, the fabric structure consists of and/or the fibers consist of an elastic material. In this way, it is achieved that the fibers are aligned automatically to their specified position extending continuously radially from the filament after passage through the catheter. The fibers can be joined with the filament by means of a mechanically producible suture. This makes possible a particularly simple production of such stents.
In order to seal the stent in an optimal way relative to the body vessel, it is appropriate to dimension the lengths of the fibers, e.g., in connection with treatment of aneurysms, such that the interweaving of these fibers preferably projects into the corresponding vessel outpocketing and in this way a reinforced thrombosis occurs in the region of the vessel outpocketing. It is also conceivable that the fibers project preferably radially into the inside of the stent, in order to form an anastomosis with a stent lying approximately thereunder. The connection to a second inserted stent is better sealed with this further embodiment of the invention.
The implantation of a stent and its positionally-correct placement can be facilitated by providing at least one filament with special markings, which facilitate the observation of the stent by remote fluoroscopy. However, other diagnostic observation methods are also conceivable, such as, e.g., magnetic resonance tomography or ultrasound.
As an alternative to the above-named forms of embodiment, in which the inner region of the stent is enclosed by a double-spiral structure, the stent according to claim 38 has a double-spiral structure in which essentially parallelly running filament wires at predetermined intervals form coiled loops opposed to one another each time along the longitudinal extent of the stent. The outer radius of the stent is determined by the radii of the loops. During the implantation, the loops are laid out in the stretched state on the otherwise longitudinally extended stent body. At the site of implantation, the loops preferably comprise superelastic or thermo-memory material are then aligned relative to their implantation. Like the previously described forms of embodiment, this stent may also be surrounded by a membrane of elastic material and the filaments of the stent can be joined to one another again by means of sleeves.
It is particularly advantageous if the stent is implanted with an implantation device. First, a catheter is inserted into the body vessel to be treated. The catheter is dimensioned such that both the stent as well as a special pushing device arrangement comprised of two pushing devices can be inserted into the body vessel. The pushing-device arrangement consists of an outer and an inner pushing device. The outer pushing device has a diameter that corresponds to the inner diameter of the introduction catheter, and also has approximately the same outer circumference as the stent in its introductory state, thus approximately the total circumference of the longitudinally extended filaments that are inserted. By means of this pushing device, the stent is advanced through the catheter up to its predetermined site in the body vessel, where it assumes its predetermined state, i.e., with the double-spiral structure of the filaments. A borehole extends axially through the outer pushing device, through which a second, inner pushing device is displaced. The latter, which is a thin pushing device produced, however, of a rigid material, e.g., Nitinol(copyright), has means at its distal end, with which it can be joined with the distal end of the stent.
By introducing the stent in its extended state into a body vessel, the latter is advanced in the catheter by means of the outer pushing device. When the stent exits from the catheter, i.e., when several loops of the double spiral have already formed in the vessel, the stent is held in the vessel coaxially by means of the inner pushing device. A springing back or a springing forward of the stent in the body vessel can be avoided in this way. An exact placement of the distal stent end in the body vessel is also possible in this way. The distal stent end is also held in its place by the thin pushing device, if the catheter is pulled back and/or the stent is advanced by the outer pushing device. Alternatively, the stent can also be pulled into the body vessel, after placement of the catheter, by means of the inner pushing device, which is joined with the distal stent tip. In this way, the stent is extended axially during the implantation procedure, whereby the friction between filaments and catheter wall is reduced. Only when the stent is completely introduced into the body vessel is the thin pushing device released from the stent tip. It is possible in principle to place the stent in the body vessel only by means of one of the pushing devices; however, the combination of the two pushing devices makes possible a particularly exact and disturbance-free implantation and placement of the stent in the body vessel.
A screw thread serves as an advantageous joining means between the inner pushing device and the stent, which is arranged preferably at the distal end of the inner pushing device, and which engages in the corresponding fastening means of the stent, i.e., one of the loops formed at the distal end of the stent by the two spirals of the double spiral. Of course, the stent can also have appropriate fastening means at its distal end, i.e., in the form of a threaded borehole adapted to the thread of the pushing device. Alternatively, hooks that correspond to one another and are arranged on the tip of the stent and the pushing device may also be used. It is also possible to join the stent and the pushing device with one another by a special soldering process, which can be triggered in the body by an appropriate electrical current. Such a principle is already applied in the case of embolization coils.
In a number of treatments, it has turned out that the lumen of a body vessel remains open after some time, even without the support of a stent. It is thus appropriate to provide devices, by means of which, the stent can be removed again from the vessel after some time. For this reason, the stent can be joined in a detachable manner with the outer pushing device. As a joining material, a threaded screw connection can be used again, or, possibly a holding clip, which is arranged at the proximal end of the stent and which can be grasped with the corresponding hook of the pushing device. It is thus not necessary to leave the pushing device in the body during the entire time of stent placement. After a predetermined time, the stent can be withdrawn from the body vessel through the catheter by the outer pushing device.
If the filaments of the stent are comprised of a material with thermo-memory properties, the latter should be implanted by a catheter filled with cooling liquid, in order to avoid the circumstance that the stent wire springs into the more voluminous spiral shape inside the catheter and thus prevents the implantation, due to the friction between the stent wire and the inner wall of the catheter.
As an alternative to the means named above, which involves two pushing devices, for the implantation of the stent according to the invention, in which a pushing device that can be introduced into the body vessel by means of a catheter is provided on its distal end with a support means for supporting the stent inside the catheter.
As a particularly advantageous support means, a fork arranged at the distal end of the pushing device is provided, which engages the filaments with its tines at the crossover points or connections or at the sleeves joining the filaments together during the implantation, and thus makes possible a particularly secure guidance of the stent in a positionally-correct implantation in the body vessel.
In another advantageous further embodiment of the invention, a forceps device is provided as a proximal support means, by means of which the filaments or the sleeves joining these filaments with one another are rigidly grasped during the implantation of the stent, but after an axial activation of the catheter, are detached from the latter. In this way, the stent can be withdrawn in the direction of the catheter, in case an erroneous placement should occur.
In another advantageous further embodiment of the invention, the support means of the pushing device are shaped like a hook and the stent has a sleeve joining the filaments together at its distal end, in which a notch is impressed, which can be joined with the hook in a form-fitting manner and is axially stationary inside the catheter. This form of embodiment is also characterized by a particularly reliable guidance of the stent during implantation.